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a
Most primitive multicellular animals and have cellular level of organisation.
b
Canal system present. Water enters through ostia in the body → central cavity spongocoel → goes out through osculum.
c
Canal system helps in food gathering, respiratory exchange and removal of wastes.
d
Fertilisation is internal, direct development
answer is D.
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Detailed Solution
In sponges, fertilisation is internal and development is indirect having a larval stage which is morphologically distinct from the adult. Sponges are primitive multicellular animals and have cellular level of organisation.They have a water transport or canal system. Water enters through minute pores (ostia) in the body wall into a central cavity, spongocoel, from where it goes out through the osculum.The pathway of water transport is helpful in food gathering, respiratory exchange and removal of waste.